如何在查詢中加入映射表

Question

我有一個查詢正在嘗試提取表中的所有問題。

問題帖子主題主題映射

我的標簽表設置有第三個表，用於將問題ID與主題ID進行映射。

但是，如何使用JOIN語句拉出存儲在主題表中的主題名稱

所以基本上我不知道如何在僅獲得主題ID而沒有主題名稱的表上執行JOIN語句

SELECT questions.* 
     , posts.post
     , COUNT(posts.post) as total_answers
     , posts.votes
     , posts.id as post_id
     , posts.created
     , users.id as user_id
     , users.username, users.rep
     , topics.name
FROM questions
LEFT JOIN posts ON questions.id = posts.question_id
LEFT JOIN users ON questions.user_id = users.id
LEFT JOIN topics ON topic_mapping.question_id = questions.id
GROUP BY questions.id

非常感謝

Answer 1

您需要先將問題加入映射表。

SELECT questions.* 
     , posts.post
     , COUNT(posts.post) as total_answers
     , posts.votes
     , posts.id as post_id
     , posts.created
     , users.id as user_id
     , users.username, users.rep
     , topics.name
FROM questions
LEFT JOIN posts ON questions.id = posts.question_id
LEFT JOIN users ON questions.user_id = users.id
LEFT JOIN topic_mapping ON questions.id = topic_mapping.question_id
LEFT JOIN topics ON topic_mapping.topic_id = topics.id
GROUP BY questions.id